High resolution or high bandwidth monochromator

ABSTRACT

A high resolution or high maximum bandwidth monochromator is provided with certain control means for controlling one jaw of an intermediate slit pair, and other control means for independently controlling the jaws in each pair of entrance, exit and intermediate slits, the monochromator being useful for exploratory research work as well as routine analysis.

United States Patent [1 1 Hawes July 24,1973

HIGHRESOLUTION'OR HIGH BANDWIDTH 2,940,355 6/1960 Cary 356/75MONOCHROMATOR OTHER PUBLICATIONS [75] Inventor: Roland C. Hawes,Monrovia, Calif. Pierce: McMath Solar Telescope of Km Peak 73] Assignee:Cary Instruments, Monrovia, Calif. tional a ry, pp p VOL 3, 12, Filed:Nov. 1971 December 1964, pages 1,313 741,346 21] A l. No.: 194,7 PrimaryExaminer-Ronald L. Wibert Assistant Examiner-F. L. Evans v 52 vs. Cl.356/101 f white Hzfefllger 51 Int. Cl G0lj 3/04, 601 3/18 [58] Field ofSearch 356/75, 88, 89, 93-101; [57] ABSTRACT 350/271 A high resolutionor high maximum bandwidth mono R i d chromator is provided with certaincontrol means for e fences controlling one jaw of an intermediate slitpair,.and UNITED STATES PATENTS other control means for independentlycontrolling the 2,587,451 2/1952 Farrand 350/271 X jaws in each pair ofentrance, exit and intermediate 2,698,410 12/1954 M e e a1 356/96 Xslits, the monochromator being useful for exploratory v research work aswe" as routine analysis 3,414,354 12/1968 Sregler 356/75 3,586,442 Tripp356/101 10 Claims, 11 DrawingFigures HIGH RESOLUTION OR HIGH BANDWIDTHMONOCHROMATOR BACKGROUND OF THE INVENTION This invention relatesgenerally to spectrophotometry, and more particularly concernsadvancements in emission type monochromators used primarily influorescence spectrophotometric instrumentation.

In general, there are two characteristically different applications forfluorescence spectrophotometers, such applications imposing quitedifferent demands on the instrumentation. Thus, for exploratory researchwork, the emission monochromator should be capable of fairly goodresolution, say one nm or better, when used to obtain emission spectra;however, when used to obtain excitation spectra or for routineanalytical purposes, the monochromator should have the maximum bandwidthconsistent with effective exclusion of the exciting radiation, i.e., atleast 100 nm. At the same time, the monochromator should haveonlymoderate width entrance and exit slits to permit convenient focusing ofthe optical beams external to the monochromator and entering into andemerging from it.

SUMMARY OF THE INVENTION It is a major object of the invention toprovide an emission type monochromator having good resolution forexploratory research work, and also having maxi- A to define successivesections of a double monochromatoroperable to isolate a band ofwavelengths with high.

and low limits,

b. beam dispersing means in the beam path between the entrance andintermediate slits and between the inwhich is independently adjustable,as-by a first control,

to, increase and decrease theiwidth of said band by changing only one ofthe'limits.

In this .regard, only the longwavelength limit of the band is forexample adjustable, as by varying the intermediate slit. The widthofthelatter in the case of a monochromator having collimator focal lengths ofabout 40 centimeters may be controllable between less than one-half and25 millimeters. Further, the beam typically comprises scatteredradiation produced by impingement of sourcemonochromatic radiation upona sample, in addition-to fluorescent radiation, and the intermediate jawadjustment is characterized in that ,excitation wavelength radiationscattered from the sample is excluded from passage through theintermediate slit throughout the adjustment. 1

Additional objects and advantages include the symmetrical location ofthe entrance and exit slit forming means, the beam dispersing means andthe beam reflecting means with respect to the intermediate slit to slit;and the employment, as beam reflecting means, of a pair of diagonalmirrors between which the beam is reflected for passage through theintermediate slit, and an optionally usable beam chopper movable in thebeam path between the diagonal mirrors.

These and other objects and advantages of the invention, as-well as thedetails of an illustrative embodiment, will be more fully understoodfrom the following description and drawings, in which:

DRAWING DESCRIPTION DETAILED DESCRIPTION Referring firstto FIGS. 1-3,jaw means includes jaws l0 and 11 defining an entrance'slit S jaws 12and 13 defining intermediate slit S and jaws l4 and 15 defi'n' ing exitslit 85. Such structure may be considered as defining successivesections of a double monochromator. operable to isolate a bandofwavelengths with high and low limits, 7 i

The illlustrated a multiple slit monochromator further includes .beamreflecting means as for example may take the form of sphericalcollimating mirror 16, in the beam path between the entrance and exitslits. Also beam dispersing means, as for example single plane grating'17, extends in the beam path between the entrance and interrnediateslits, and'in the beam path between the'intermediate and exit slits.Further, that 'grating is characterized by opposed directions ofdispersion in the 'successive' monochromator sections, the first-0fwhich is associated with'the beam path between S, and S and the secondof which is associated with the beam path between S, and S The completebeam path isshown in principleray form as including ray 15a passing fromdefine a double pass monochromator characterized by subtractive,dispersion; the provision of the beam dis- S, tothe mirror forreflection at 18, ray 15b passing from the mirror to the grating fordispersion, ray',1 5c passing from the grating'to the mirror 16 forreflection at 19, ray, 15d extendingfro m the mirror, to the diagonalNewtonian'mirror N, for, reflection at 20', my 15c extending from mirrorN, through "slit S, and'to' di'ag onal Newtonian mirror N, forreflection at 21, my 15f extending from mirror N, to the mirror 16for'r'eflection as ray 15g returning to the grating 17 and ray 15hextending from the grating to the mirror for reflection as ray 151'passing through slitSg. In this regard, rays 15a 15d, and apart of ray15 extending from mirror N, to the plane of the intermediate slit 8,,may be considered as first pass rays, while rays which include the 26(which may be a laser) and passes through optical elements 27 which mayinclude a quarter wave retarder and an electrooptic modulator, asdescribed in copending application Ser. No. 192,815 by Ahmad Abu-Shumays and Jack J. Duffield and entitled Linear Polarization ApparatusFor Use In Circular Dichroism Polarimetry. The radiation exiting fromthe monochromator and shown schematically as ray 15] passes to aphotodetector and associated electronics and recording mechanismindicated at 28, and described in US. Pat. No. 3,013,194 to l-LI-I.Cary. A rotating beam chopper 70 proximate slit S, may be used toprevent detection of light scattered toward the exit slit on the firstpass through the monochromator, by providing for A.C. detection, asdescribed in US. Pat. No. 2,652,742 to A. Walsh.

In accordance with an important aspect of the invention, one jaw of theintermediate slit S, is made independently adjustable to increase anddecrease the width of the transmitted radiation band; and, typicallyonly the long wavelength limit of the band is so adjustable. Referringto FIG.4, control means 29 is operable to simultaneously adjust jaws ofall the slits S,, S, and 8,, whereas control means 30 (graduated innanometers bandwidth) is operable to independently adjust only one jawof slit 8,. Thus, as seen in FIGS. a and 50, when control 29 isoperated, all the slits may be simultaneously widened, with both jaws ofeach slit moving away from a center line defining a nominal wavelength.Such center lines are indicated at 31-33. In the other hand, whencontrol 30 is operated, and as appears from comparison of FIGS. 5a and5b, only jaw 13 is moved away from nominal center line 32, all otherjaws remaining unmoved. Jaw 12 remains unomved by control 30 so as toexclude exciting radiation throughout the adjustment of jaw 13. The samefunctioning appears from comparison of FIGS.5c and 5d.

In FIG. 6, the FIG. 5a condition of equal slit widths S, S, S, isfurther represented by the narrow pass band 32 of scattered fluorescenceradiation from a sample, the wavelength of the exciting radiationappearing at 33. When S, is increased in relation to S and S, as in FIG.5b, the widened pass band for S, appears as at 34 in FIG. 6. Similarly,the FIG. 50 condition of equal and widened slit widths is represented bythe band-35; whereas, when S, is increased as in FIG. 5d, the widenedpass band for S, appears as at 36, in FIG. .7.

In one representative monochromator embodying the concepts of FIGS. 1-3,the width of the intermediate slit S, is variable from less thanone-half mm to about 25mm. The Newtonianmirrors are large enough toaccept the 25mm wide beam. To avoid vignetting, it

may be desirable to provide a field lens shown as 65 in FIG. 8 at theintermediate slit, and large enough to accept the full beam when theslit is 25 mm wide. The field lens renders the aperture stops in thesuccessive sections of the monchromator optically conjugate. In theexample chosen, the monochromator has 4 nm/mm reciprocal dispersion whenthe intermediate slit matches the entrance and exit slits in width, oris narrower. Widening the intermediate slit S, increases the bandwidthof the monochromator unsymmetrically with respect to the nominalwavelength, without changing the proportion of stray to accepted light.This assumes a narrow band fluorescence excitation source,

and that the fluorescence is white, or of constant energy, over thebandwidth.

In the modified form of the instrument seen in FIG.

8, separate gratings 40 and 41 are employed in two entirely separatesections of a double monochromator, and at opposite sides of a plane 42defined by the intermediate slit S,, and usually provided with a mask ator near this plane to prevent radiation from passing from onemonochromator section unto the other by any means other than through theslit 8,. Jaw 43 of the intermediate slit forming means is movablerelative to jaw 44, by the control as seen at 30 in FIG. 4. Jaws of allslits 3,, S, and S, are simultaneously movable as by the control means29 of FIG. 4. Note that a beam entering S, is defined by a principle ray46 between S, and mirror 47, ray 48 between mirror 47 and grating 41,ray 49 between grating 41 and mirror 50, ray 51 reflected from mirror 50to Newtonian mirror 52, ray 53 reflected from mirror 52 to Newtonianmirror 54 via slit 8,, ray 55 reflected from mirror 54 to mirror 56, ray57 reflected to grating 40, ray 58 transmitted from the grating tomirror 59, and ray 60 reflected to and through exit slit 8,.

In FIGS. 1-3 and 8, the gratings may be rotated about an axis locatedapproximately in the face" of the grating, and normal to the planes ofeach of FIGS. 2 and 8, as by the schematically illustrated actuators 61,and 61a and 61b, to control the wavelength of radiation transmitted viathe exit slits. The gratings 40 and 41 may, for example, have 600 linesper millimeter, be'oriented to the substractive dispersionconfiguration, and be mounted on separate, counter-rotatingtables.

A field lens 65 proximate slit S, accepts the full beam when slit 8, hasmaximum width, as described previously.

In this double monochromator configuration it is'ordinarily notnecessary to locate abeam chopper at the intermediate slit, the mask ator near center line 42 being effective to prevent light scattered towardslit S,

on passage through the first monochromator section from reaching S,except such small proportion as may unavoidably accompany beam 53through slit 8,.

I claim:

1. In a monochromator, the combination comprising a. means formingentrance, intermediate and exit slits to define successive sections of adouble monochromator operable to isolate a band of wavelengths with highand low limits, and

b. beam dispersing means in the beam path between the entrance andintermediate slits and between the intennediate and exit slits, andcharacterized by opposed directions of dispersion in the successivesections, r said intermediate slit forming means including first andsecond jaws, the first jaw carried to be independently adjustablerelative to the second jaw to increase and decrease the width of saidband by changing only one of said limits, the entrance and exit slitforming means also including pairs of jaws,

d. first control means connected with said first jaw to control saidindependent adjustment thereof, and

e. other control means connected with said entrance,

intermediate and exit slit forming means to simultaneously vary thewidths of the entrance, intermediate and exit slits independently of thefirst control means by movement of both jaws of each slit forming means,the connection of the first control means with the first jawcharacterized in that said independent adjustment thereof may be madeseparate from the variation in intermediate slit width effected by saidother control means.

2. The combination of claim 1 in which only the long wavelength limit ofthe band is adjustable by varying the intermediate slit.

3. The combination of claim 1 wherein said intermediate slit width iscontrollable within a range of from less than one-half millimeter toabout 25 millimeters.

4. The combination of claim 1 including a source of excitingmonochromatic radiation impinging upon a sample so as to producescattered radiation, including radiation shifted in wavelength from thewavelength of excitation, said scattered radiation producing said beam.

5. The combination of claim 1 including a field lens proximate saidintermediate slit to accept the full beam when the intermediate slit hasmaximum width.

6. The combination of claim 1 including beam reflecting means in'thebeam path between the entrance and exit slits and wherein said entranceand exit slit forming means, said beam-dispersing means and said beamreflecting means are symmetrically located with respect to saidintermediate slit to define a double pass 9. The combination of claim 8wherein said beam refleeting means includes apair of diagonal mirrorsbetween which the beam is reflected for passage through the intermediateslit, and a beam chopper movable in the beam path between said diagonalmirrors.

10. The combination of claim 4 wherein said intermediate jaw adjustmentis characterized in that excitation wavelength radiation scattered fromsaid sample isexcluded from passage through the intermediate slitthroughout said adjustment.

1. In a monochromator, the combination comprising a. means formingentrance, intermediate and exit slits to define successive sections of adouble monochromator operable to isolate a band of wavelengths with highand low limits, and b. beam dispersing means in the beam path betweenthe entrance and intermediate slits and between the intermediate andexit slits, and characterized by opposed directions of dispersion in thesuccessive sections, c. said intermediate slit forming means includingfirst and second jaws, the first jaw carried to be independentlyadjustable relative to the second jaw to increase and decrease the widthof said band by changing only one of said limits, the entrance and exitslit forming means also including pairs of jaws, d. first control meansconnected with said first jaw to control said independent adjustmentthereof, and e. other control means connected with said entrance,intermediate and exit slit forming means to simultaneously vary thewidths of the entrance, intermediate and exit slits independently of thefirst control means by movement of both jaws of each slit forming means,the connection of the first control means with the first jawcharacterized in that said independent adjustment thereof may be madeseparate from the variation in intermediate slit width effected by saidother control means.
 2. The combination of claim 1 in which only thelong wavelength limit of the band is adjustable by varying theintermediate slit.
 3. The combination of claim 1 wherein saidintermediate slit width is controllable within a range of from less thanone-half millimeter to about 25 millimeters.
 4. The combination of claim1 including a source of exciting monochromatic radiation impinging upona sample so as to produce scattered radiation, including radiationshifted in wavelength from the wavelength of excitation, said scatteredradiation producing said beam.
 5. The combination of claim 1 including afield lens proximate said intermediate slit to accept the full beam whenthe intermediate slit has maximum width.
 6. The combination of claim 1including beam reflecting means in the beam path between the entranceand exit slits and wherein said entrance and exit slit forming means,said beam dispersing means and said beam reflecting means aresymmetrically located with respect to said intermediate slit to define adouble pass monochromator having subtractive dispersion.
 7. Thecombination of claim 6 wherein said beam dispersing means is defined byseparate gratings at opposite sides of a plane dfined by saidintermediate slit.
 8. The combination of claim 6 wherein said beamdispersing means is defined by a single grating for dispersing the beambefore and after beam passage through the intermediate slit.
 9. Thecombination of claim 8 wherein said beam reflecting means includes apair of diagonal mirrors between which the beam is reflected for passagethrough the intermediate slit, and a beam chopper movable in the beampath between said diagonal mirrors.
 10. The combination of claim 4wherein said intermediate jaw adjustment is characterized in thatexcitation wavelength radiation scattered from said sample is excludedfrom passage through the intermediate slit throughout said adjustment.